The general focus of this proposal is on the mechanisms that govern neuronal differentiation. Our studies are centered on ME1, one of the basic-helix-loop-helix (bHLH) transcription factors which are known to be essential for normal brain development. A mental disorders including schizophrenia and depression, among others, are believed to have a large genetic contribution, it is likely that the studies in this proposal will have an impact on our understanding of mental disorders, their causes and their treatments. We recently cloned cDNAs corresponding to the mouse E-box binding proteins (MEs). Two of these MEs, ME1a and ME1b are the result of alternative splicing of the ME1 gene. These transcriptional regulators are related to Drosophila bHLH protein Daughterless. Because of the strong homology of ME1 with transcription factors essential for cell determination and differentiation in the nervous system in Drosophila, and because of the characteristic mRNA expression pattern of ME1 in areas of the nervous system where neuronal differentiation occurs; it is likely that it plays an important role in development of the nervous system. The goal is to further characterize ME1 in order to understand its function during neuronal differentiation. The specific aims ar to determine the spatial and temporal expression of ME1 proteins and to study their molecular and cellular mechanism of action. ME1 functions as a dimer and as heterodimer. The genes regulated by ME1 are thought to be the results of the dimerization partner. Therefore, it is most important to identify and characterize the cellular proteins that interact with ME1 and to identify the neuronal genes regulated by these bHLH transcription factors. Recently, we have detected ME1 heterodimer partners (MHPs) in brain nuclear extracts. In addition, our results indicate that the GAP-43 promoter is regulated by ME1 in an E-box dependent manner. GAP-43 is a neuronal specific growth associated protein. Studies are proposed that will begin to define the structure- function and transcriptional characteristic of ME1 and MHPs. Together, these studies will help to define the molecular and cellular properties of ME1 and MHPs and significantly advance our knowledge of neuronal differe iation.